Hybrid cars and electric vehicles carry large size batteries to run the vehicle's own bodies. The hybrid cars and electric vehicles are also equipped with air-cooling blowers to cool their electric circuits including the large size batteries. For the air-cooling blowers, a cooling capacity is specified such as an airflow quantity necessary from time to time according to an amount of electric current supplied to an electric circuit, the running condition, and the like of the vehicle. The air-cooling blower needs to be controlled to satisfy the cooling capacity. Variations in the cooling capacity depend on the air-cooling blower. In particular, the variations in the cooling capacity depend largely upon variations in rotation speed of an impeller (bladed wheel).
A motor for driving the air-cooling blower is required to be rotated stably in order to cool the large size battery steadily. The following control method is available, in general, as a technique of driving a motor stably at a target rotation speed. That is, an actual rotation speed of the motor is detected with a position detecting sensor or the like device capable of detecting a rotating position of the motor. The rotation speed of the motor is then controlled in a manner to minimize a difference between detected actual rotation speed of the motor and the target rotation speed of the motor.
In a case of a three-phase brushless motor controlled by pulse-width modulation (hereinafter referred to as “PWM”) drive, start timing for driving individual elements to execute the PWM drive is controlled based on outputs of three position detecting sensors composed of hall elements and the like devices. Therefore, the rotation speed of the motor cannot be maintained stably if there is a deviation in the positions where three position detecting sensors are mounted.
To overcome the above problem, patent literature 1 discloses a structure, as one example, that comprises a positional deviation storage means for storing an amount of deviation in position of the rotating position detecting sensor from a proper position of the sensor, as measured beforehand, and a rotating position signal correction means for correcting a rotating position signal of the rotating position detecting sensor according to the amount of positional deviation stored in the positional deviation storage means.